The present invention relates to an image pickup apparatus capable of changing lenses and an interchangeable lens to be detachably mounted thereon.
As disclosed in Japanese Patent Laid-Open No. 2-65474, many image pickup apparatuses capable of changing lenses such as single-lens reflex digital cameras and video cameras perform focus control based on a focus evaluation signal showing a contrast state of an image obtained using an image pickup devise such as a charge-coupled device (CCD) sensor. Such a method for controlling focus is referred to as a contrast detection method.
Further, many image pickup apparatus mount a, so called, live view display function for displaying a picked up image in a substantially real time on a display. Japanese Patent Laid-Open No. 2000-50141 discloses an image pickup apparatus that starts the live display view function after controlling a focus for obtaining an image somewhat in focus at an object distance from a distant view to a close view after a power is turned on.
Generally, focus control by a contrast detection method searches a position at which a focus evaluation signal extracted from a picked up image is largest while a focus lens is moved. Thus, it takes time to obtain an image in focus, compared to that by a phase difference detection method.
Therefore, for example, when changing lenses with a structure for picking up an image determined using a tripod, it is necessary to wait until the image in-focus is obtained to start picking up the image to perform all over again the focus control by the contrast detection method from the beginning.
Unlike the image pickup apparatus as disclosed in Japanese Patent Laid-Open No. 2000-50141, it is difficult for an image pickup apparatus of a changing-lenses type on which various lenses are to be mounted to perform the focus control for picking up an image somewhat in focus at an object distance from the distance view to the close view.